1. Field of the Invention
The disclosure generally relates to an antenna structure, and more particularly, to a wideband antenna structure for use in a mobile device.
2. Description of the Related Art
With the progress of mobile communication technology, portable devices, such as notebook computers, tablet computers, mobile phones, multimedia players, and other hybrid functional portable devices, have become more common To satisfy the demand of users, portable devices usually can perform wireless communication functions. Some devices cover a large wireless communication area; for example, mobile phones use 2G, 3G, LTE (Long Term Evolution) and 4G systems and use frequency bands of 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, 2300 MHz, and 2500 MHz. Some devices cover a small wireless communication area; for example, mobile phones use Wi-Fi, Bluetooth, and WiMAX (Worldwide Interoperability for Microwave Access) systems and use frequency bands of 2.4 GHz, 3.5 GHz, 5.2 GHz, and 5.8 GHz.
In conventional designs, a fixed-size metal element is often used as a main antenna body in a mobile device, and the length of the metal element should be equal to a half of wavelength (λ/2) or a quarter of wavelength (λ/4) which corresponds to the desired frequency band. However, since the metal element for the generation of low-frequency bands requires a longer resonant path, it is difficult to design the metal element in the limited inner space of a mobile device.